Electronic storage of digital image data prior to subsequent processing has been used for many years.
One prior art image storage method for use in systems which process multiple digital images involves using multiple image delays connected in series. Input data is fed into the first delay element, the output of the first delay element is fed into a second delay element, and so on. The outputs of all the delay elements along with the input data are then available for subsequent processing such as filtering.
Another prior art method for multiple image storage uses a large memory device (i.e. memory array) with enough storage locations (addresses) for two or more images. Image data is stored sequentially in the memory array, and retrieved at a later time for downstream processing. This method requires multiple read operations to retrieve all of the desired data from each of the individual images stored in the memory array. Multiple read operations require a very high speed and costly memory array and additional logic circuits to control the reading from multiple addresses.
As discussed above, prior art methods have been used in downstream image processing applications. One such application involves converting a series of film frames to video. To convert a 24 Hz film to 60 Hz interlaced video, the individual film frames are first scanned and separated into two video fields (A and B). Unlike live video, these two fields are not temporally displaced; fields A and B can be displayed in either order as they both contain material captured at the same time. Following this step, the film fields are displayed one after the other, alternating between A and B with an extra field inserted every four fields. This process is called 3:2 pulldown, so named for the number of video fields "pulled down" from each film frame (three fields from Frame 1, two fields from Frame 2, etc.). The resulting field rate becomes 60 Hz which can be easily transferred to videotape.
The prior art techniques discussed above do not allow for variations in the input data rate without affecting the output image processing rate. It is well understood that variations in data rates are common in video and graphics sources, especially if the original source is in an analog format (such as a VCR) or communicated over a bus. In addition, the prior art techniques result in a delay between input and output which is an integral number of image delays. In some cases it is desirable to have a non-integral or variable amount of delay between input and output, such as in temporal filtering between multiple images or in frame rate conversion, as discussed above. Furthermore, in some circumstances minimum latency from input to output may be required.
The following prior art is considered pertinent to the present disclosure:
U.S. Patent Documents 4,876,596 - Faroudja Oct 24/89 Film-to-video converter with scan line doubling 4,987,551 - Garrett, Jr. Jan 22/91 Apparatus for creating a cursor pattern by strips related to individual scan lines 5,008,838 - Kelleher, et al. Apr 16/91 Method for simultaneous initial- ization of a double buffer and a frame buffer 5,257,348 - Oct 26/93 Apparatus for storing data both Roskowski, et al video and graphics signals in a single frame buffer 5,321,809 - Aranda Jun 14/94 Categorized pixel variable buffering and processing for a graphics system 5,550,592 - Aug 27/96 Film mode progressive scan Markandey, et al. conversion 5,598,525 - Nally, et al. Jan 28/97 Apparatus, systems and methods for controlling graphics and video data in multimedia data processing and display systems 5,604,514 - Hancock Feb 18/97 Personal computer with com- bined graphics/image display system having pixel mode frame buffer interpretation